Unerupted teeth cannibalizing their neighbors: part 1

Published: March 2016

Bulletin #53 March 2016

Unerupted teeth
cannibalizing their neighbors: part 1

For the most part in the dental
development of a child, the first permanent maxillary molar erupts in its due
time, at the dental age of 6-7 years.This is 4-5 years before the deciduous second molar is due to exfoliate
and before the second premolar should erupt. An aberration of this normal
developmental process occurs when an erupting maxillary first molar becomes
entrapped in the sub-gingival distal concavity that is the cemento-enamel
junction of the crown and roots of the deciduous second molar.1

Fig. 1a. Lateral jaw radiograph of the right
side of a 7 year old child with an ectopic maxillary first molar impacted under
the distal of the second deciduous molar and causing marked resorption of the
distal side of the roots (arrow).

Fig. 1b. A follow-up radiographs after treatment
with a simple removable appliance that has distallized the permanent
molar.Note the degree of loss of root
tissue of the second deciduous molar.

In this situation, resorption of this
subgingival area of the root of the deciduous tooth will occur and will proceed
to a varying degree, depending on the angulation of the eruptive path of the
permanent molar (Fig. 1). In many of these cases, there is a mesial inclination
of the permanent tooth, not usually present in normal development. Experience
indicates that this is more likely to be seen in children with a short
maxillary dental base and large molar teeth – both permanent and deciduous.

As the result, much or all of the
disto-buccalroot of the deciduous molar
will disappear in the resorptive process, but the distal enamel portion of the
crown of the tooth will remain and may become hollowed out as its dentine
interior disappears (arrow). This then becomes a complicating factor, since it
forms an unresorbed ledge which effectively arrests further occlusal migration
of the permanent tooth. Because it is the mesial corner of the occlusal surface
of the permanent molar which comes into contact with the enamel ledge of the
deciduous molar, any further expression of eruptive potential will exacerbate an
existing mesial orientation of the long axis of the tooth. Because further
resorption may cause the disappearance of its distal root, the deciduous second
molar may also tip mesially and its distal aspect extrude, as the result of the
eruptive push from above.

There are many instances of loss to
the resorptive process of the distal half of the root and much of the interior
of the crown, leaving the area that was originally the cervico-enameljunction to end up as a knife edge of
undermined enamel. Nevertheless and even despite these unfavorable
circumstances, the tooth is entirely asymptomatic and its extraction is to be
discouraged as far as possible. The reasoning behind this advice is as
follows:-

1.The unerupted second premolar now has very little resistance to
its very premature downward eruptive migration and it can sometimes be seen to
have descended into the partially evacuated enamel shell of the crown of its
deciduous predecessor. However the premolar at this stage has virtually no root
and its early eruption is to be prevented if possible, so that a substantial
root length may develop while the tooth is still protected within its
developmental follicle. Extraction of the deciduous molar will accelerate its
eruption in a rudimentary, delicate and endangered state!

2.Loss of the deciduous molar encourages the permanent molar to
complete its eruption and encourages an unrestrained drift forward in a
mesially tipped condition, which also brings its apex forward. This represents
a degree of mesial translation. Therefore, distally tipping the tooth into an
upright state will not now relocate it in its ideal position, since it will now
require some distal bodily movement if adequate space is to be reclaimed for
the premolars and canine.

3.Even assuming that space may have been completely regained in a
phase 1 treatment and the molar is in a good class 1 relation with its
antagonist, space maintenance will be an essential ingredient in the 4-5 year
follow-up period until the first premolar and canine have erupted.

But is non-extraction a practical alternative?
This would require moving the permanent molar distally and freeing it from
under the deciduous molar.The
literature in orthodontics and in pediatric dentistry is replete with methods
of achieving this and many interesting, customized gadgets and devices have
been described. These will not be discussed in the present bulletin.

What are the benefits of de-impacting
the permanent first molar in its ectopic location and leaving the deciduous
tooth in place?

1.Movement of the permanent molar is begun while the tooth is
relatively high in the alveolus, with the deciduous molar preventing its mesial
and vertical movement. Therefore, a minimal degree of distal tipping only is
needed to relocate it to its ideal position.

2.Leaving the second deciduous molar in its place obviates the
need for artificial space maintenance.

3.Even markedly resorbed distal roots in these cases do not
necessarily condemn the tooth to an early demise. For the most part, they will
remain in place and asymptomatic for their full designated duration.

Can resorption be equated with
dental caries?

When caries reaches the pulp,
infection is introduced into a tissue which cannot express the swelling
associated with its natural inflammatory reaction because it is enclosed within
a closed pulp chamber. It thus causes pulp strangulation and pulp death,
usually accompanied by considerable pain.

There is a very narrow wall of
dentine of the root that separates the PDL of a deciduous molar from its dental
pulp, which means that very little resorption of the root will need to occur
before the resorption front reaches the pulp. When there is root resorption, many
practitioners will immediately assume that, when this point is reached, there
will be an emergency pulpitis, equating the situation with that occurring when
a carious process within the tooth reaches the pulp. As a consequence, their mistaken
treatment of choice will likely be to advise extraction of the affected tooth –
a conclusion not in agreement with an understanding of the biological facts.

In contrast, resorption is a
sterile process and the breakdown of the dentinal wall between connective
tissue surrounding the root and the pulp chamber causes the cellular elements
of the PDL and the pulp to merge and to undergo a progressive metaplasia. This
is not accompanied by inflammation, swelling or pain and, as the resorption
continues on, the pulp chamber opens up further with vital connective tissue of
the subgingival layers becoming contiguous with the pulpal tissue.

In such a circumstance, the pulp is
no longer enclosed in a solid casing and, although deep caries may still cause an
infective inflammatory reaction of the underlying pulpal/gingival tissue, an
acute pulpitis can no longer occur. At the gingival extremity of the crown of
the deciduous molar, only the enamel resists resorption, while beneath it
dentine is resorbed. As the result, the unresorbed enamel edge of the crown of
the tooth comes to sit on the gingiva. The fact that the practitioner may be
able to probe this enamel edge is evidence that that part of the interior of
the crown is open to the intra-oral environment and, therefore, to saliva-borne
bacterial infection. Nevertheless, pain and inflammation are not commonly
associated. If the permanent molar is moved distally and freed from its
impaction, the resorption ceases and the situation can usually remain stable
for several years.

Can resorption of the roots of
deciduous and permanent teeth be equated?

In the above paragraphs, I have
presented an overview of resorption in relation to the shedding of deciduous
teeth, as a (rather long) preface to the more important subject of this month’s
bulletin. With this apparently unconnected preamble, I would like to draw a
parallel between this well-known debacle between an erupting permanent tooth
and its deciduous neighbor and the resorption of the roots of erupted permanent
teeth adjacent to and seemingly caused by impaction of an unerupted tooth.

There is no distinction between the
character, quality or histology of the tissues when dental pulp meets
resorptive PDL and that occurring between the pulp and surrounding connective
tissue associated with the resorption of an incisor due to the impaction of the
adjacent maxillary canine. They are one and the same and, while the first is a
completely physiologic process, the latter is considered a pathologic process,
simply because root resorption is not a desirable nor accepted characteristic
of a permanent tooth. It would be convenient to be able to characterize or
identify the differences that may exist between a deciduous tooth that does
resorb and a permanent tooth that does not, but the factors involved in this
quirk of nature have, to date, resisted discovery.

With the rapid evolution of imaging technology from planar
two-dimensional radiographic representation, through rotational tomography to spiral
computerized tomography and cone-beam computerized tomography, accuracy and
reliability of diagnosis of resorption of incisor roots by an aberrant
unerupted canine has leaped from 12%2, 3 through 38% of lateral
incisors and 9% of central incisors affected to a greater or lesser extent, i.e.
47% of affected individuals, in total,4.to
66.7% of adjacent lateral incisors and 11.1% of adjacent central incisors
affected,5 respectively. Obviously, it is the initial and the minor
resorptive lesions that had previously evaded detection that now form the
majority of those discovered by the new technology and it is certainly
pertinent to add that the finding is largely of little clinical significance.
However, it should be remembered that all the severe resorption cases started
“life” as seemingly minor lesions!

Fig. 2a. The anterior portion of a panoramic
view shows the superimposition of the unerupted permanent canine on the lateral
incisor and the severe root resorption.

Fig. 2b. A CBCT cross-sectional cut across the
lateral incisor to show the relation of the superimposed labial canine and the
severe and oblique nature of the resorption.

Fig. 2c. A CBCT axial cut shows the close
proximity of the canine to the severely resorbed incisors.

It is well
documented in the literature that this variety of root resorption will almost
completely arrest once the offending “aggressor” tooth has been distanced from
the immediate vicinity, either by extraction or by orthodontic movement6The severe incisor root resorption (SIRR) cases,
with a third or more their root already lost (Fig. 2a-c), have been shown to
have a predilection for females.7It should come as no surprise thatthe affected teeth have a marked degree of mobility.
Nevertheless, moving the canine away from the immediate area will result in a remarkable
improvement in the condition of the incisor.

Fig. 2d. A periapical radiographic view of the
treated case on the day of debonding.

Fig. 2e. A follow-up radiograph 3.8 years post
treatment. The bonded retainer was placed for orthodontic retention rather than
periodontic splinting, which had been considered unnecessary. The lateral tooth was
vital and firm.

The radiographic follow-up in
these cases provides clear evidence of a change from a rarified and radiolucent
area around the shortened root end to a re-condensation of trabeculated bone
and a convincing reduction of the mobility (Fig. 2d, e), without the need for
periodontal splinting. Thus, following successful orthodontic treatment, one
may justifiably look forward to a very much brighter view of a future for these
compromised teeth (Fig. 3).

Fig. 3b. A periapical view of the left side
showing the condition at the time the canine was distanced from the area.

Fig. 3c. At the completion of treatment and
prior to debonding, these periapical views show total absence of bone support
for the lateral incisors, which were highly mobile. Splinting was advised for
both orthodontic retention and periodontal support.

Fig. 3d. At 5.6 years post-treatment, the periapical
views show positive condensation of trabeculated mature bone around the short
root ends. Vitality and tooth color were maintained and the teeth showed greatly reduced mobility.

The resorption of a
small portion of the root end, so-called “blunting” with the loss of 2-3mm of
root length during orthodontic treatment, is something that would not unduly
alarm us, because we see this in our routine non-impaction and straightforward
orthodontic cases. Because of the angle at which the canine approaches the root
of the incisor in the impaction cases, resorption is usually oblique and if the
canine is fairly high and mesially displaced, this causes an oblique slicing of
the apical third of the root.

Question #1
What should we do if we see that the canine has superimposed itself on one of
the incisors from a more lateral direction and lower down on the root, such
that the resorption damages the middle of the root? The real point of the
question is whether or not the resorption involves the pulp.

In a published
study of root resorption from this cause, Falahat et al.8 classified
resorption into three degrees of severity. Slight resorption was defined as “up
to half the dentine thickness”, moderate resorption as “midway to the pulp or more, the pulp lining being
unbroken” and severe resorption as “the pulp is exposed”..
Fully one third of the cases in the study were
classed as severe, according to these definitions i.e. the pulp has been “exposed”
by the lesion

.

Fig. 4a. The anterior portion of a panoramic
view shows obvious resorption of the lateral incisor by the impacted right
canine. This case was treated about 20 years ago and before the cone beam
tomography era. It was not possible with 2D planar radiography to assess the
degree of resorption that had occurred.

Fig. 4b. Following the successful resolution of
the canine impaction, a new periapical view of the lateral incisor indicated a
large resorption crater in the cervical region, close to the gingival margin.
Because of the real possibility of an accidental opening of the lesion to the
oral environment, root canal treatment, followed by a periodontal flap to
enable sealing off the defect, was advised.

Fig. 4c. A periapical view taken during the
root canal procedure, which had failed due to the absence of a large section of
the labial wall of the root.

Fig. 4d. Viewed from the labial and mesial sides
of the extracted incisor to show the extreme nature of the longitudinal
resorption along the full length of the labial aspect of the root, not evident
from the periapical radiograph. Today, with the advent of CBCT, this case would have been treated very differently.

In the
day-to-day practice of dentistry, when a patient with “severe resorption” is first
diagnosed, there are many forms of treatment that may be offered, largely
dependant on the specialty of the first practitioner to whom the patient turns
for treatment. Odd though it may seem, there is a real danger that most of
these prescribed treatment modalities will be inappropriate (Fig. 4)!

If an oral
and maxillofacial surgeon were to be consulted regarding a severe resorption
case as defined in that study, it is likely that the advice given would be to
extract the resorbed incisor tooth.

If an endodontist
were to be consulted, the chances are that he/she would request opening the
root canal of the resorbed incisor, extirpating the pulp and root treatment, while
attempting to occlude the lateral perforation from within.

If a
periodontist were to be consulted and assuming that adequate access could be
achieved with an open flap procedure, perhaps the plan would be to debride the
immediate area of the “exposure” and occlude the defect with glass ionomer or
other cement. At the same time, the pulp would be amputated and the patient
referred for definitive root canal therapy. If, however, the proximity of the
canine prevented access, orthodontic treatment to distance the canine might be
advised as a first step and only then a renewed attempt at occluding the defect
be made.

Days,
weeks or months may elapse between the time the diagnostic imaging will have
determined that resorption has involved the pulp and the visit to one or more
of the following : the pediatric dentist, the surgeon, the endodontist, the periodontist
or the orthodontist. During this entire period the tooth will have been
entirely asymptomatic, will have undergone no color change and even a pulp
tester will have declared it to be vital. So, I would argue that, to describe this
severe form of resorption as an “exposure”, is inexcusably alarmist and highly
emotionally charged. This smacks of paralleling the phenomenon with and
engendering the same degree of urgency as caries that has exposed the pulp. As
the result, the unenlightened practitioner may be intimidated into performing ill-advised
immediate surgical and/or endodontic treatment.

Question
2: What of the impacted canine that has caused the loss of the apical 2-3mms
of root of the incisor, which we discussed above, or where the resorption has
occurred without canine impaction? These “blunted” root cases are common and
the implication is that exposure of the pulp in the lost apical portion has
occurred, as described above. The connective tissue of the PDL comes into
direct contact with pulpal tissue, which undergoes metaplasiaand with which it merges.

We know
that, for as long as the canine remains in the location and displays its eruptive
potential, the resorption will continue. Accordingly, the first line of
treatment must be to move the canine away from the immediate area. As pointed
out above, distancing the canine effectively stops the resorptive process.
6

In order
to resolve the impaction of the canine, surgery needs to be performed to provide
the orthodontist with the access needed to assume therapeutic control. An open
surgical exposure, involving complete removal of the dental follicle and
leaving the tooth open to the oral environment at the end of the procedure will
make the chances of infection of the resorbed area extremely high and the
resultant pulpitis of the incisor difficult to avoid. It is strongly
contraindicated. Instead, a closed procedure should be chosen, with a wide attached
gingiva flap reflected, the canine bulge located and the tooth’s most accessible
surface minimally exposed through a small opening in the dental follicle. No
attempt should be made to remove the follicle, but the full flap should be re-sutured
back to its former placeonce the eyelet attachment has been bonded to the
exposed enamel surface, with a chain or twisted steel ligature exiting through
the sutured flap edge. Instrumentation of the deeper areas should be avoided.

Question
3: Having moved away the canine, should we recommend root treatment for this
resorbed incisor (Fig. 4)- perhaps anti-resorption therapy with calcium hydroxide
or sealing the defect with MTA?

In
answer to the above questions, I would conclude as follows:-

Following
successful treatment to distance the canine from the resorbing root area, we
have learned to expect that:-

1.resorption will have ceased

2.the area of contact between the
resorptive soft tissue of the periodontium and the pulp is entirely free of
bacteria, free of surgical trauma and, in consequence, free of inflammation.

3.the teeth are healthy, vital and
symptomless,

4.the teeth are vital and their color
is unchanged.

5.there is
no pathology and, therefore, no treatment is needed!

Acknowledgements: I wish
to acknowledge the learned discussions that I have had on the different aspects
of resorption and the advice that I have received from Prof. Nardi Caspi-Casap
(oral and maxillofacial surgery), Prof. Adam Stabholz (endodontics) Prof. Ayala
Stabholz (periodontics) and Professor Yossi Shapira (pediatric dentistry) in
the writing of this bulletin.

The figures in this bulletin are copyright
and appear in Becker A. Orthodontic Treatment of Impacted Teeth. 3rdedition. Oxford: Wiley-Blackwell Publishers, 2012.

In the
April 2016 bulletin, we shall continue this discussion specifically in relation
to the prognosis of the resorbed incisor, whether the affected incisor will
respond to orthodontic movement, whether orthodontic movement will re-ignite
the resorption process, how reliable will the periodontal support be and what
type of bone regeneration or bone loss can be expected in the years ahead.